Ignition systems for automotive engines are conventionally provided with an elastomeric boot for covering and protecting the electrical connection between the ignition cable and the spark plug. As engine operating temperatures have increased over the years and as the cylinder heads were located closer to the exhaust manifolds, the temperatures to which the boot and spark plug are exposed have increased correspondingly. The high temperatures reduce the useful life of the boot elastomer, even when high temperature silicone products and protective lubricants are used. In addition, the high voltage ignition systems on current engines can create conditions exceeding the dielectric strength leading to external grounding that can cause further erosion of the boot as well as corrosion of the contact interfaces. It has further been determined that the ignition cables can create high potential gradients, with attendant high E-field intensities creating corona discharges that can further degrade the boots and contacts.
In an early approach, metal shields were used to surround the spark plug boot to shield against excessive heat as disclosed in U.S. Pat. No. 4,497,532 to Benzusko et al. and U.S. Pat. No. 4,671,586 to DeBolt. The shields, however, can provide an adverse grounding path when the dielectric strength is exceeded resulting in engine misfire and performance reduction. It has also been proposed to use high temperature ceramic sleeves to isolate the spark plug boot from high operating temperatures as disclosed in U.S. Pat. No. 6,305,954 to Aluise. The sleeves are rigid and difficult to mount on existing cables, and are limited to in-line boots, to the exclusion of commonplace inclined or right angle boot configurations. The ceramic material does not assist in dissipating electrical fields. It has also been proposed to reduce corona discharge by incorporating a conductive sleeve on the boot interior as disclosed in U.S. Pat. No. 5,716,223 to Phillips et al. All of the foregoing approaches are directed to original equipment limiting the ability to provide improved protection to existing as well as new engines.
It would accordingly be desirable to provide a universal design for ready integration with existing and new ignition cables to protect the boot and electrical connection from deterioration by increasing thermal and radiant insulation, and decreasing adverse electrical effects.
It would also be desirable to provide an improved cover for the cables and boots that increases resistance of the cover to operational and mechanical degradation